The voice sounds more like Beritra's, and when Inanna puts the crown on, her eyes glow the same color as Beritra's, and her dragon-form looks like his too, from what little we can see. It seems more likely that Beritra essentially uploaded his power into Apsu's crown, and used it to possess Inanna; the currently un-modeled character in the vision could easily be an illusion, knowing Beritra, and considering that Apsu is as dead as a Dragon Lord can be. It would also make sense for Beritra of all people to have held on to Apsu's crown.
Dragon Lords CAN shapeshift, but only between 2 forms;